[RFC] consolidated libdt proposal

Haren Myneni haren at us.ibm.com
Wed Aug 9 13:19:55 EST 2006

Pantelis Antoniou wrote:

> On 08 Αυγ 2006, at 8:37 ΠΜ, Haren Myneni wrote:
>> Hollis Blanchard wrote:
>>> On Sun, 2006-08-06 at 19:38 -0500, Hollis Blanchard wrote:
>>>> Hmm, so we'll have at least three copies of this code: uboot, kernel,
>>>> and Xen. Would it make sense to put this stuff into a libdt.a?
>>>> Technically, dtc has a "libdt" already, but it's absurdly incomplete
>>>> (I don't even know why it's there), so we could just replace it.
>>> Mark, I had a look at the code Pantelis wrote for u-boot, and it was
>>> pretty easy to adapt to meet Xen's (userspace-based) needs. I've
>>> attached my version below (and see ft_setup() at the bottom of the
>>> file). Does it meet your requirements for the kernel bootwrapper?
>>> One limitation of the attached code is that it doesn't support changing
>>> the *size* of properties, though I don't think that would be too
>>> difficult to add if needed.
>>> Haren, what about using this in kexec-tools?
>> Hollis,
>> Good idea to have this lib. Based on brief look, some of these funcs 
>> are also useful for kexec-tools. Yes, as you mentioned, changing the 
>> size of properties is important for kexec/kdump.
>> Present flattened device-tree process in kexec-tools:
>> - Kexec-tool reads the /proc/device-tree and sort these entries since 
>> we get the different order than the first kernel uses.
>> - creates linux,usable-memory property under /proc/device-tree/ 
>> memory@* as appropriate. (for kdump)
>> - Modify the reserve map for RTAS, initrd, TCE and (0- crashkernel- 
>> start)
>> - Create initrd properties if not exist in the first kernel as needed
>> - Modify bootargs property
>> Thanks
>> Haren
> Hi Haren,
> Mind writing down what your requirements are? Just modifying the size 
> of the properties?


Yes, kexec-tool can use the proposed interfaces.

kexec-tool requirements:
creating the flattened device-tree from scratch based on the first 
kernel /proc/device-tree
While doing this process, should be able to
- add new properties (Ex: linux,usable-memory property under 
- Modify properties: size and the value of the property could be 
changed(Ex: bootargs, not an issue since creating new anyway)


> Note that my functions work in a two phases.
> In the first phase the tree is build with the string table being put 
> at the end
> of the allocated memory area in a downward motion.
> When the tree is finalized the string table is memmov'ed to be 
> adjacent to the structure
> proper.
> Could you use this two phased approach for you uses? I.e. first work 
> with maximum sized
> properties and perform a move & fixup stage when finalizing?
> Regards
> Pantelis
>>> If everybody can use this (I expect small modifications would be
>>> needed), I think we should turn it into a library in the dtc source
>>> tree. The various projects using it could then include snapshots (to
>>> avoid dependencies). In general I'd like to avoid everybody writing and
>>> maintaining their own version of this stuff (myself included).
>>> --------------------------------------------------------------------- 
>>> ---
>>> /

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